In fact, Goseiger would have been overall better with a different cast than what we got.
The show's cast was pretty problematic. Not in terms of being bad actors, I think, but they didn't have a lot of
presence. They didn't know how to stand like heroes or talk like heroes when the script called for it. I think it really damaged the 90s throwback thing the show was going for.
Even the goofiest of the 90s casts, like Carranger, Megaranger, or Kakuranger, knew how to carry themselves like real heroes when it was time for the fight scenes to start. If something serious happened, they could look serious for a bit. I'm not sure the Goseiger cast ever really got beyond looking like idols playing with toys, though Niwa could put in a pretty good effort when the script gave her something to work with.
That said, I think Yudai Chiba deserves some credit for trying really damn hard by the end of the series to be a proper out-of-suit Red. There's a stunt they do toward the end of the show where they stuff his team jacket with explosive packs and set it off while he falls to his knees and does a hammy NOOOOOO that was one of the better out-of-suit stunts I'd seen in Sentai in years when it first aired.
Yudai Chiba also gets through an out-of-suit fight with Gosei Knight that's pretty credible toward the end of the show, and I've seen suit actors fail to keep up with Jiro Okamoto in top form (and Gosei Knight played to all of his strengths). I know someone else suggested Watanabe Shu as a Yudai Chiba replacement, but I can't see him pulling off either of those stunts credibly.
I certainly didn't see anything top those Goseiger action scenes for out-of-suit stuntwork until Gokaiger brought Junya Ikeda into the cast. Every time they give that kid out-of-suit stunts to do, I'm just blown away. He even kept up with Keiichi Wada in a fight scene worthy of Dairanger! If they just wrote him into every show for the next ten years, I would be okay with that.